The principle of a semiconductor solar cell is described as follows.
A solar cell device generates electron-hole pairs after it receives light. The electron-hole pairs are separated by an electric field built into the device, and then guided outwards by two metal electrodes of the device. In this way, a phenomenon of charge flow appears to provide a current. Thus, as long as the energy gap of a material is suitable and formation of the electric field possible, the material may be used for manufacturing a solar cell.
A few decades ago when semiconductor solar cells were manufactured and researched, a variety of materials for the solar cells were developed, such as homo- and hetero- p-n junctions, metal-insulator-semiconductor diodes, metal semiconductor diodes, etc.
No matter which kind of material is used for manufacturing a solar cell, the materials receive light at their principal surfaces to generate the photoelectric conversion effect. Thus, specific metal contact patterns are required, whereby the cost is increased. Furthermore, the aforementioned conventional solar cell structures have p-n junctions which are fabricated in the presence of costly and poisonous gases. For example, AsH.sub.3 and B.sub.2 H.sub.6 are respectively used as n- and p-type dopants, and SiH.sub.4 is used for the deposition of amorphous silicon. In short, the conventional solar cells have disadvantages of not only high manufacturing cost but also bad effects on the environment.